The purpose of this project is to study the biochemical events associated with development, plasticity and involution of the nervous system. We have used the quantitative autoradiographic [1-14C]leucine method to study the sites of origin and the process underlying changes in nervous system organization that take place during these events and the [14C]deoxyglucose method to examine the outcome of the changes, i.e., the functional reorganization that has occurred. Our studies of normal development in rats show decreasing rates of protein synthesis in most brain regions from day 14 to the adult stage except in the paraventricular and supraoptic nuclei of the hypothalamus. We are studying two model systems of plasticity: (a) the developing monkey visual system, and (b) the developing and adult mouse somatosensory system. Results of our studies of chronic monocular deprivation in monkeys early and late in the critical period show that the biochemical response that may underlie the functional reorganization of the striate cortex is a decrease in the rate of protein synthesis indicative of a decrease in the growth rate in deprived geniculate cells. Results of deoxyglucose studies on the effects of whisker follicle removal in neonatal mice show that when the lesioned mice reach adulthood metabolic maps in both somatosensory cortex and in trigeminal brainstem nuclei are altered. When adult mice are similarly lesioned metabolic maps in the cortical barrel field are also found to be altered after 160 days. These results indicate functional reorganization in both the neonatal and the adult whisker-barrel pathway in the mouse and they suggest that this system may serve as a useful model of both developmental and adult plasticity.